As governments around the world increase the use of wind farms to reduce dependence on fossil fuels, many are grappling with a similar problem: wind farms cause interference to radars. That often puts a need for green energy at odds with a country’s need to monitor, protect and defend its airspace.
A Lockheed Martin TPS-77 radar, located at Trimingham in East Anglia, is being used by the UK Ministry of Defence (MoD) to mitigate the effects of the Sheringham Shoal wind farm, which is off the east coast of England.
The radar’s success is the result of a partnership between Lockheed Martin, Serco, and the UK MoD, plus the support of the wind industry, the Department of Energy and Climate Change and The Crown Estate. This long-term collaboration has also resulted in extensive knowledge transfer and industrial participation.
The United Kingdom initially purchased one TPS-77 ground-based, long-range air surveillance radar system to monitor the country’s airspace and to address the growing presence of windfarms. Subsequently the UK MoD implemented two more TPS-77 radar systems. Lockheed Martin has also upgraded two existing Type-92 radars with the same wind farm mitigating capability.
“The fundamental issue is that wind farms are designed to be high and exposed to take advantage of available wind,” said Carl Newman, UK TPS-77 programme manager with Lockheed Martin. “At the same time, radars are positioned high to provide the greatest coverage, which results in radars and wind farms being placed in sight of each another. When they are in the same coverage area, the spinning blades of the turbines significantly interfere with radar returns. This can lead to the potential report of an aircraft where there is none or prevent the detection of an actual aircraft.”
It’s all in the design
The Lockheed Martin solution reduces the effects of complex wind farm clutter without requiring additional “infill” radars. The fundamental solution lies in the TPS-77 radar’s design. Many radars use multiple stacked beams to detect a target and estimate its height. However, that design does not always allow the radar to distinguish between planes, turbines and other ground-level clutter based upon height. Other systems rely on numerous radars positioned around the observation point to provide a comprehensive aerial picture, which can cause many logistical issues.
Lockheed Martin solved the problem by using a 3-D pencil beam architecture with advanced signal processing. This allows transmit and receive beams to independently separate aircraft from wind turbine returns.
“It’s like using a laser versus a flashlight,” said Carl Newman. “The stacked beam radars are like a floodlight, which illuminates a room by spreading the light far and wide, reflecting everything at the same time. Our pencil beam system acts more like a scanning laser, allowing localised reflections of the surveillance area while minimizing the impact from a nearby windfarm.”
While the Trimingham TPS-77 radar is the first to achieve full operating capability in the UK, Lockheed Martin has tested the capability to solve wind farm interference in the State of Texas as well as in Denmark. Lockheed Martin’s long-range radars have a proven performance record, with more than 170 of this family of radars in operation worldwide, many of which have performed for decades in remote, inhospitable areas and in a wide range of operational environments.
“We’ve seen just about every type of clutter you can see, and we’ve tested TPS-77 radars from the arctic to the equator,” said Newman. “We’ve yet to encounter a situation that these radars can’t perform. They consistently display a high probability of detection while maintaining low false alarm rates. Now that same design reduces the effects of complex wind farm clutter”.